Condenser tube



Patented Apr. 11, 1939 UNITED STATES PATENT OFFICE CONDENSER TUBE NoDrawing. Application December 24, 1936, Serial No. 117,563

Claims.

vision of a condenser tube of improved physical characteristics that maybe readily fabricated, worked and welded, and which has an improvedresistance to the corrosive action of industrial Waters and reagents.

Condenser tubes formed of 70:30 cupro-nickel have long been recognizedas highly suitable for use in condensers subject to corrosion. Applicanthas found that if small amounts of vanadium are added to thecupro-nickel its resistance to corrosion and the facility with which thetube may be welded, flanged or otherwise worked to secure it to the tubeplate or the like are much increased. Further, this addition of a smallamount of vanadium markedly increases the tensile strength and hardnessof the tube, as compared to one made of binary cupro-nickel of the samenickel content. This increase in tensile strength and hardness, asidefrom being in themselves desirable in respect to increasing thedurability of the tube, is desirablein that it tends to inhibit the typeof corrosion termed stress corrosion".

It has been found that the liability of a condenser tube to corrosion isincreased by the presence in the metal of the tube of oxide particles.These particles tend to form nuclei about which corrosion is initiated.Vanadium applicant has found has the efifect of eliminating the presenceof such oxides.

Condenser tubes are particularly subject to failure by a combination ofchemical corrosion and mechanical erosion loosely termed impingementcorrosion, Impingement corrosion com monly occurs near the entrance ofthe tube. Water, for example, conducted by the condenser tube commonlyenters it from a chamber with which the end of the tube directlycommunicates. The end of the tube thus constitutes an orifice from thechamber, and although the tube is of uniform diameter causes the waterto enter the tube in the form of a jet of contracted cross-section. Thisjet inwardly from the end of the tube expands to the inside dimensionsof the tube followed by a region of turbulence extending along the tubeuntil the flow becomes quiescent. The space about the jet is filled withair and other gases liberated from the water because the jet tends tocreate a reduced pressure in that space. This air tends to mix into thewater at the region of turbulence. Because the inner walls ,of the tubeat the space surrounding the jet are wet with the medium beingconducted, and because there is a mechanical scouring of the tube at theregion of turbulence, and in both instances the medium is rendered of anoxidizing nature on account of the air and other gases, 9. mostnoticeable corrOsion tends to occur at these portions of the tube.Applicant however has found that the introduction of vanadium into thetube alloy acts to inhibit this type of corrosion. Further, he has foundthat if in addition to vanadium small amounts of chromium are added theresistance of the tube to this type of corrosion is further increased.The vanadium apparently imparts to the metal of the tube the property offorming a tenacious corrosion resisting film on the surface of the tubewhen initially subjected to the action of an oxidizing medium, thefacility with which this film is formed and its tenacity apparently being increased by the presence of chromium.

Preferably the amount of vanadium added to :30 cupro-nickel should notexceed 1%, best results being secured-with a range of vanadium fromabout 0.1 to 0.9%, and maximum effects with about 0.5% vanadium.Satisfactory results are secured with amounts of chromium up to about1%, although amounts up to 2% are not particularly objectionable. Withabove 2% chromium the alloy is dimcult to work into tubes. The preferredalloy consists of 70:30 cupro-nickel containing 0.5% each of vanadiumand chromium.

The amount of nickel may be varied between 20 and 40%, the amount ofvanadium being not less than 0.15% for values of nickel under 26%.Otherwise the amounts of vanadium and chromium may be as specified inconnection with 70:30 cupro-nickel.

It has been found that sulphur, if present in the alloy of which thetube is made, has a deleterious effect on account of the formation ofnickel sulphide. To eliminate this effect preferably manganese is addedto the melt. Manganese has a greater affinity for sulphur than hasnickel. The manganese sulphide and small amounts of residual manganesehave no deleterious efiect on the properties of the tube. Preferably theamount of manganese present in the tube should not exceed 0.5%, althoughamounts up to 1% are not particularly objectionable. If no sulphur ispresent in the materials entered into the melt of course manganese neednot be employed. However, preferably it is employed to insure againstany possible deleterious effects that may be caused by the possiblepresence of sulphur. It will therefore be understood, that although inthe appended claims manganese is not specified, the tubes defined bythose claims may within the scope of the latter contain amountsmanganese up to 1% of the alloy, it being understood that manganese inthe sense that it imparts no direct beneficial eilect may be consideredas an impurity.

Tubes made of the alloys described, besides having an increasedresistance to corrosion, greater strength and hardness, and greateradaptability in respect to being worked and welded, may be fabricatedmore easily than cupro-nickel of the same nickel content. The tubes maybe formed by drawing and extruding processes, and require lighterequipment to produce them than the cupro-nickel tubes of the same nickelcontent. In the sense that the tubes are formed by working the alloy asdistinguished from casting them they are in the appended claims termedwrought tubes.

Although not precluded, the presence of metals such as aluminum, ironand zinc preferably is avoided, as these metals tend to have adeleterious effect on the resistance of the tube to corrosion, andfurther tend to reduce the strength and toughness of the tubes and, insome instances, to make them brittle. Aluminum has a marked tendency todecrease the ease with which the tubes may be welded,

It will further be understood that within the scope of the appendedclaims other metals may be present as impurities, or may be deliberatelyadded for imparting special characteristics, so long as they do notsubstantially destroy valuable properties tended to be imparted by thevanadium or vanadium and chromium.

I claim:

1. Wrought tubes of cold workable cupro-nickel alloy containing chromiumand vanadium, and capable of forming on their surfaces exposed to themedia conducted thereby a tenacious protective film the presence ofwhich is indicated by a resistance to impingement corrosion greater thanthat of a tube of binary cupro-nickel of the same copper and nickelcontent, which alloy contains, approximately. 20 to 40% nickel,appreciable amounts up to 1% vanadium, but at least 0.15% vanadium forall amounts of nickel up to 26%, appreciable amounts up to 2% chromium,balance substantially copper.

2. Wrought tubes according to claim 1 containing, approximately, 26 to40% nickel and 0.15 to 1% vanadium.

3. Wrought tubes according to claim 1 containing, approximately, 0.5%each of vanadium and chromium.

4. Wrought tubes according to claim 1 containing, approximately, 30%nickel,

5. Wrought tubes according to claim 1 containing, approximately, 30%nickel and 0.5% each of vanadium and chromium.

- RICHARD A. WILKINS.

